1. Field of Invention
The present invention is concerned with a bus arrangement for interconnecting circuit chips each having at least one input port and one output port, using optical waveguides, and with an optical waveguide switch for cooperation with electronic circuit chips.
2. Description of Prior Art
Semiconductor integrated circuits have experienced a significant growth in the density of components and in the complexity of functions per chip. The trend towards very large scale integration (VLSI) continues and the cost per function decreases due to the batch processing of wafers. However, with increasing complexity the pin-out per chip also increases. This causes an increase in cost and a degradation of performance on two levels:
On the chip-packaging level, the chips are handled individually. With increased pin-out the handling cost for bonding wires to chip pads, and packaging cost increase.
On the module level, several chips have to be interconnected on a printed-circuit board to perform the function of a complete system, e.g. a microprocessor system. With increase pin-out per chip, the size of the package and the number of interconnecting lines are also increased. This has several undesirable effects:
The layout of the circuit board becomes more complex, hence increasing design time and cost. The average distance between pins becomes longer causing an increased delay in signal propagation. Also, the stray capacitance and noise pick-up of the signal lines becomes worse.
It is therefore desirable to have a signal transfer arrangement for interconnecting circuit chips on a board which is not subject to above disadvantages of electrical distortion by noise and stray fields, and which needs no contact bonding but which allows high packing densities and is suitable for large quantity production.
Utilization of optical transmission technology for this purpose would be particularly desirable.
In an article by L. Balliet et al "Module-to-module Communication Via Fiber-Optic Piping", published in the IBM Technical Disclosure Bulletin, Vol. 22, No. 8B, January 1980, pp. 3519-3520 it was suggested to use fiber-optic paths or waveguides in circuit cards to interconnect modules. The article shows only a single connection and does not disclose how high packing densities and multidrop (bus) connections for interconnecting a plurality of modules can be achieved. Furthermore, it is necessary to integrate light sources (LED or laser) into the modules which is disadvantageous, particularly if many interconnections, i.e. many sources are required.
Optical switches for selectively switching light between optical fibers or waveguides are known, e.g. from following patents and publications: (a) U.S. Pat. No. 3,208,342 (A. H. Nethercot) "Electro-optic Light Coupling of Optical Fibers"; (b) E. G. Lean: "Optical Switch and Modulator in Parallel Waveguides", IBM Technical Disclosure Bulletin, Vol. 17, No. 4, September 1974, pp. 1210-1213; (c) R. V. Schmidt: "Guided Wave Optical Devices Using Ti-diffused LiNbO.sub.3 ", Proceed. Electro-optic System Design Conference, New York, 1976, pp. 557-560; (d) H. P. Hsu et al: "Flip-chip Approach to Endfire Coupling Between Single-mode Optical Fibers and Channel Waveguides", Electronics Letters, Vol. 12, No. 16, Aug. 5, 1976, pp. 404-405; (e) U.S. Pat. No. 4,035,058 (M. Papuchon) "Electro-optical Switch and a Method of Manufacturing Same", (f) O. Mikami et al: "Directional Coupler Type Light Modulator Using LiNbO.sub.3 Waveguides", Technical Digest 100C 1977, pp. 161-164; (g) M. Papuchon: "Electrically Active Optical Bifurcation", Technical Digest 100C 1977, pp. 165-168; (h) B. Chen et al: "Thin Film Optical Switch", Technical Digest 100C 1977, pp. 173.
All these papers and patents describe how light can be controllably coupled from one optical fiber or waveguide into another. None of them suggests, however, how a great number of closely spaced interconnections can be made between a plurality of circuit chips on a module.
Coupling between optical fibers or waveguides without switching control is known, e.g. from U.S. Pat. No. 3,994,559 (J. D. Crow et al) "Bidirectional Guided Mode Optical Film-fiber Coupler", and from the publication of E. A. Ash: "Leaky Wave Couplers for Guided Elastic Wave and Guided Optical Wave Devices", IBM Technical Disclosure Bulletin, Vol. 15, No. 1, June 1972, pp. 309-310. Both do not show how many closely packet interconnections can be made between chips or modules each having a great number of input and output ports.